Panoramic cameras are called upon to provide images over three hundred and sixty (360) degrees of selected near and far-field subjects in such a manner that the images recorded thereby are substantially free from smearing as the camera pans the subject and are neither underexposed nor overexposed given the way the ambient light illuminating the subject may vary at different angular positions about the three hundred and sixty degree pan. To provide the ability to select which vertical portion of the subject is to be recorded, provision should be made to allow for framing of the subject. To provide the ability to select the extent of the subject that is to be recorded, provision should be made to allow for the use of different field (or angle) of view lenses, such as fisheye, wide angle, normal and telephoto lenses. If, in addition, such a camera were portable, rugged, reliable, easy to use, inexpensive, compact, and lightweight, it would appeal both to amateur and professional photographers alike.
A periscope-type panorama camera that addresses the problem of image smearing is disclosed by McNeil in U.S. Pat. No. 2,794,379. It includes a cylindrical camera body having spaced apart top and bottom circularly shaped walls that are joined by a cylindrical side wall to provide a light tight enclosure. Film is wrapped along the inside of the cylindrical focal plane of the side wall and a film guide and an advance mechanism are provided to guide and advance the film about the cylindrical focal plane after each exposure.
The top wall is journaled for rotation within the cylindrical side wall and has a central post that is keyed to a motor driven axle located at the center of the cylindrical camera body. As the axle is turned by a motor or other mechanism, the top plate rotates about the axis of rotation of the axle relative to the cylindrical side wall.
A periscope assembly defining an optical axis is mounted for rotation with the rotatable top plate of the cylindrical camera body such that its optical axis is parallel to, radially displaced from and contained in a plane common to it and the central axis of rotation. The periscope includes a lens. First and second mirrors each to either side of the lens are adjustably aligned along the optical axis to place its nodal points on the axis of rotation for a given focal length and object distance.
The lens is mounted in an aperture provided in the top wall of the cylindrical camera body. The focal length of the lens is made equal to the radius of the cylindrical side wall of the camera body. The radius of the cylindrical side wall defines the focal length of the lens. For different focal lengths differently sized housings are required.
The first mirror of the periscope assembly (below the lens) is mounted at forty five degrees to the optical axis in the camera body so as to confront the rear nodal point of the lens and the cylindrical focal plane. Both the lens and the first mirror must be separately adjusted to align the virtual image of the rear nodal point on the axis of rotation. To do so, the first mirror is axially adjusted along the optical axis until it squarely confronts the cylindrical focal plane and is permanently keyed into position. The lens is then axially adjusted in its mounting aperture until the distance between its rear nodal point and the first mirror equals the distance by which the optical and rotational axes are displaced. These adjustments are laborious and time consuming and require that the cylindrical body be disassembled.
The second mirror of the periscope assembly (above the lens) in one embodiment is a roof prism that is mounted outside the camera body confronting both the front nodal point of the lens and the subject. The roof prism is required to reverse the image. In an alternative embodiment, a mirror is substituted for the roof prism and a relay lens is required to reverse the image. In either embodiment, the element is axially adjusted until the distance between it and the front nodal point of the lens is such that the virtual image of the front nodal point of the lens appears to lie on the axis of rotation.
To provide for different fields of view, differently sized mirrors and/or lenses would need to be implemented. The change in the size of the first mirror might require a different radial offset between the optical and rotational axes. Thus a different, specially constructed camera body would be required. The change in the focal length of the lens could also require a differently sized cylindrical side wall. Again, a specially constructed camera body would be required. The roof prism, or second mirror in the alternate embodiment, excludes a wide angle of view because the optical path is folded across the orientation of the exposure slit. For the mirror embodiment, where the relay lens is required to reverse the image, the angle of view is further limited because the combination of lenses excludes far off-axis rays.
No provision is made, or able to be made, for framing the subject. To provide for different object distances for a given focal length, the housing as well as the periscope assembly would need to be disassembled, and two adjustments made for the first mirror and a third adjustment made for the second mirror to re-effect the alignments of the virtual positions of the front and rear nodal points of the lens onto the actual axis of rotation. No provision is made for the effects of varying ambient lighting conditions as the camera pans the subject.
An underwater panoramic camera that addresses the problem of image smearing given an object distance and fixed focal length is disclosed by McNeil in U.S. Pat. No. 3,141,397. The camera includes a cylindrical camera body having circular top and bottom plates that are joined by an annular lens that constitutes the side wall of the cylindrical camera body. An arm having a radially extending lens barrel defining an optical axis on one side and a film guide and feed assembly on its other side is rotatably mounted in the cylindrical camera body such that as the lens barrel end of the arm is turned about the axis of rotation in one angular direction the film guide and feed assembly on the other side of the arm advances film in the opposite angular direction.
The in-line lens system, which includes the expensive and fragile annular lens of the cylindrical side wall of the camera body and the optical elements of the in-line lens barrel itself, provides a fixed focal length and a given object distance. To prevent smearing as the in-line barrel pans for a fixed focus and given object distance, the center of rotation of the arm is positioned so that the ratio of the eccentricities of the front and rear nodal points of the lens is made equal to the ratio of the object distance to the image distance.
There is, however, appreciable smearing for subjects at other object distances. To prevent smearing for subjects at other object distances, the housing needs to be disassembled and another in-line lens assembly with the proscribed center of rotation for each different given object distance installed. In addition, no provision is made, or able to be made, for changing the framing of the subject, and no provision is made, or able to be made, for changing the field of view.
The radial dimension of the cylindrical housing body depends on the fixed focal length of the lens. Different focal lengths would thus require different, specially manufactured housing bodies. No provision is made for the effects of varying ambient light as the camera pans.
An in-line panoramic camera with an off-axis lens that addresses the problem of image smearing is disclosed by Cummins in U.S. Pat. No. 3,311,038. The camera is like that of the '397 patent except that it has a stationary film guide and advance assembly defining an image surface and has an arcuate, cylindrical-segment lens that constitutes but a part of the side wall of the camera. As in the '397 patent, the in-line barrel lens is rotated about a preselected point (center of rotation) that is between the front and rear nodal points of the lens selected such that the ratio of the eccentricities of the front and rear nodal points is made equal to the ratio of the object distance to the image distance for a given object distance and focal length.
In one embodiment where the rear nodal point of the lens confronts the image surface, a pair of mirrors is provided therebetween that decreases the distance from the center of rotation of the arm of the in-line lens to the image surface by an amount that equals the eccentricity of the rear nodal point from the point of rotation of the lens, and in another embodiment where the front nodal point confronts the image surface, a prism is provided therebetween that increases the distance from the center of rotation of the arm to the focal surface by an amount that equals the eccentricity of the rear nodal point. In either embodiment, however, different, specially designed and manufactured lens assemblies need to be provided for different given object distances. The focal length of the lens is made equal to the radius of the stationary film guide and feed assembly. Different, specially constructed housing bodies are required for different focal lengths. No provision is made, nor is able to be made, for changing the field of view and/or the framing of the subject. No provision is made that accounts for the effects of varying ambient light conditions.
An in-line and fixed focus panoramic camera that addresses the problem of controlling exposure for the way the light varies about a panoramic subject is disclosed by Waroux in U.S. Pat. No. 3,246,588. In one embodiment, single panoramic images are provided and in another stereo panoramic images. In either embodiment, an in-line lens subassembly having a fixed focus and an optical axis is mounted for rotation with a camera housing with its optical axis offset from a stationary drum of a film guide and feed subassembly that is journaled for rotation about the axis of the camera housing. In either embodiment, no provision is made to take account of the blurring that results from the offset of the optical axis of the lens subassembly from the axis of rotation and no provision is made for framing, for different focal lengths and their correspondingly different fields (angle) of view, or for selectable near- and far-field object distances.
To control exposure, in one embodiment one of one or more cams having differently shaped profiles and/or a cam of variable profile is pre-selected to drive the camera housing about its axis of rotation with a speed that corresponds to the profile of the cam selected. In this embodiment, the cam that is pre-selected is the one that is judged best in the field to match the prevailing lighting conditions. In another embodiment, the cam that is selected is set to control the size of the diaphragm of the lens subassembly rather than the speed of rotation. Again, once selected, the way the diaphragm is varied with angle is pre-set. In a further embodiment, a light meter is used to change either the speed or the size of the diaphragm point-to-point.